They say helmets don't make people safer, and enforcement of the law appears arbitrary.

But New Zealand crash victim Grace Nicholls knows all too well what can happen if you're not wearing a helmet.

"The helmet absolutely saved my life."

Ms Nicholls had a near-death experience when she fell off her bike and into the path of an oncoming car.

"My head hit the oncoming traffic, there was a car coming and then I went underneath the car - and had I not been wearing a helmet, I think it would've been a very different story," she told The AM Show.

Ms Nicholls says the biggest piece of her helmet that her parents found on the road was the size of a 50 cent coin.

"The whole thing just exploded... I can't imagine what would've happened had I not been wearing a helmet."

She believes choice is important but compulsory helmet laws for cyclists are a no-brainer.

"It's not worth the risk and I think it should remain mandatory for people to wear helmets."